Watch these tiny 3D printed quadruped robots pronk their way over rough terrain

Jun 10, 2016 | By Benedict

Researchers from the University of Maryland have used 3D printing to develop tiny quadruped robots capable of navigating rough terrain. The 3D printed robots, weighing under 2 g and measuring just 20 mm long, can move with different gaits, including trotting, waddling, bounding, and pronking.

Insects are given a hard time by humans. Capable of incredible feats of strength and movement, insects are still more likely to find themselves under a flyswatter than a microscope. That could all change soon, however, as more and more roboticists are starting to build tiny, insect-like robots which mimic the clever and unusual movements of those most forsaken of creatures.

Ryan St. Pierre and Professor Sarah Bergbreiter of the University of Maryland, for example, have been busy creating their own sub-2 g robo-insects with a 3D printer, and last month presented a paper on the gait characteristics of those robots at the International Conference on Robotics and Automation (ICRA) in Stockholm, Sweden. In the paper, which has been published in IEEE Robotics and Automation Letters, the two experts explain how they experimented with the gaits of their tiny robots in order to see which were the most effective at traversing normal and difficult terrain.

The Maryland researchers used a 3D printer to print each robot in one go, before removing all support material and then embedding a 2-mm neodymium cube magnet into each of the bot’s four hips. By rotating a larger magnet nearby, the researchers could then cause the robots to start moving, and could adjust the dipole orientation of each hip magnet to alter the gait of the bot.

Despite their bug-like size and appearance, the tiny robots are actually less like insects than they could have been. The researchers originally built the robots with six legs, making them similar in appearance to the Robotic Autonomous Crawling Hexapod (RoACH) robots built by researchers at UC Berkeley in 2009. St. Pierre and Bergbreiter, however, found that the six legs constantly locked together. The solution was to remove a pair of legs, making the coin-sized bots quadrupeds instead of hexapods.

After finalizing their robot design, the researchers were able to ask the big question: just what is the most effective way for a tiny 3D printed robot to move? Walk? Skip? Drive? Thanks to their clever magnetic actuator setup, St. Pierre and Bergbreiter were able to test a variety of animal-like gaits in order to find out. Each 20 mm x 5.6 mm robot, equipped with four “whegs” (wheel-leg hybrids) was configured to trot, waddle, bound, and even pronk—a straight-legged leap most commonly performed by springboks—over normal and difficult terrain, with the researchers able to measure the robots’ success in each case.

As the headline of this piece might have suggested, pronking, otherwise known as “stotting” or “pronging”, came out on top: when the 3D printed robots were programmed to move with a pronking gait, actuated at 10 Hz, they were able to travel with an average top speed of 78 mm/s, almost four body-lengths per second. Pronking was the fastest gait over normal and mildly rough terrain, while other gaits performed slightly better over very rough terrain.

“We have learned that more dynamic gaits, where there is more pitching of the body as it locomotes, are more effective crossing over rough terrain, but are slower on flat terrain,” St. Pierre told IEEE. “It was most surprising to find that there were some flight phases in some of the gaits, such as pronking. This flight phase is what helped that gait outperform other gaits over flat terrain.”

According to the researchers, this study was just the beginning. Thanks to the simplicity of the design, it is easy to change the robot’s legs, gait, and body shape, all of which can radically affect how the tiny robo-insects move. Best of all, the researchers can 3D print a whole swarm of the tiny robots at once using a multi-material 3D printer, and—by using new materials—can shrink the robots down to an even tinier size.

“It’s always a fun challenge to try to make robots as small as possible,” St. Pierre said. “Currently, I am working on making a robot, of the same design, that would be 2.5 mm long, an order of magnitude smaller than the ones we presented at ICRA. Smaller robots can more easily go places that later robots can’t, and having them in various sizes would increase their utility.”

So there you have it: tiny 3D printed robots that look like bugs and can leap like a springbok. Next time you think about squishing a bug, take a look at what it’s doing—it might just inspire you to build the next generation of robots.